The disclosure relates generally to turbine engine variable bleed valves and, more particularly, to such valves used to prevent surge and remove of foreign matter from the primary or core flow path proximate the compressor inlet.
Gas turbine engines can suffer from combustion instability problems when large quantities of unwanted particulates, such as ice, ice crystals, water droplets, sand and dust, enter the core particularly when the engine is being operated at low power and low thrust operating conditions which are established when the engine is operated at idle.
To ensure optimum compressor performance and efficiency and alleviate the ingestion of such particulates into the core, it is well known in the gas turbine engine field to provide variable bleed valves (VBVs). Known VBVs are typically configured as outwardly (or inwardly) configured doors that open to provide a bleed flowpath to bleed off compressed air between the booster and core engine compressor of gas turbine engines. In doing so, unwanted particulates are drawn out of the core flowpath and into the bleed flowpath, and more particularly a bleed exhaust duct. The air is often bled from what is referred to as a gooseneck flowpath between the booster and core engine compressor. Aircraft fan jet gas turbine engines, and marine and industrial derivatives of such engines, have employed various forms of curved flowpaths and VBV bleed doors that are retracted into the flowpath casing so as to form an entrance to a bleed duct that bleeds booster or low pressure compressor discharge airflow and draw particulates out of the flowpath in a manner such as that disclosed in U.S. Pat. No. 4,463,552 entitled “Combined Surge Bleed and Dust Removal System for a Fan-Jet Engine” by Monhardt et al.
In one known configuration, opening and closing of the bleed duct is conventionally provided by a circumferentially disposed plurality of pivotal doors that open outwardly so as to retract into the engine structure or casing and are operated by a single unison ring powered by one or more fuel powered actuators. An example of such a system using a retracting pivotal door is disclosed in U.S. Pat. No. 3,638,428 entitled “Bypass Valve Mechanism” by Shipley et al. and assigned to the same assignee as the present invention and incorporated herein by reference. The operation of the VBV is scheduled by the engine controller, either a mechanical or digital electronic type may be used.
Problems associated with conventional bleed valve ducts and valve doors often occur in the form of pressure loss and exhaust gas temperature (EGT) upset. In particular, in current outward (and inward) VBV door designs, pressure loss is inevitable, especially when opening the VBV at cruise in order to extract ice crystals and shed ice from the booster vanes and blades. The airflow in current design is normally bled into a large cavity via one or more valve doors, prior to being discharged into a duct to the fan bypass hence incurring pressure loss. In addition, larger particulates and larger amounts of particulates such as ice require larger doors, resulting in larger pressure losses and larger actuator mechanisms to operate the larger doors. To avoid pressure losses, it is highly desirable to remove ice, ice crystal, water droplets sand and dust from the gooseneck, or core flowpath without removing core airflow or minimizing the amount of core airflow that is removed. It is additionally desirable to re-design the VBV within structural cavity constraints (bulkhead, actuator mechanism, exhaust duct and piping) while maintaining operability, capability and particulate extraction efficiency, as compared to state-of-the-art inward/outward door VBV design.
Thus, it is highly desirable to provide a bleed air valve, and an engine incorporating the bleed air valve, that includes the ability to remove unwanted particulates, such as ice, ice crystals, water droplets, sand and dust, from a compressor airflow and efficiently bleed air between the booster and a core engine compressor without incurring detrimental pressure losses or exhaust gas temperature upset.